The human respiratory system is basically made up two lungs, located inside the upper part of the body cavity. Lungs increase the gas exchange surface area while minimizing the evaporation. However, the gas exchange takes place deep in the lungs, in alveoli, which are found at the end of a long series of tubes. The series of tube begins from the mouth and nose. The inhaled air first passes the throat, followed by the larynx, then the trachea. At the end of the trachea, it divides into two branches; the left and right bronchus, and each bronchus lead into a lung. Each bronchus again divides into many branches forming a network of tubes, which ends with smaller tubes called bronchioles. The trachea, bronchi, and bronchioles are collectively known as tracheobronchial system. The entire tracheobronchial system is made up of three layers; mucosa, submucosa, and fibrocartilaginous layer. The proportions of all these three layers vary at each step; for example, the bronchioles do not contain cartilaginous layer.
The lower end of trachea divides into two main branches forming the left primary bronchi and right primary bronchi. These main branches are quite smaller in diameter than the trachea and have the same structure as the trachea. Each main bronchus runs into its lung where it divides again into many branches forming a network of bronchi that extend into the lobes of the lung. Each time the bronchi divide, they become smaller and thus able to carry air to every corner of the lung. These smallest ends of bronchi finally form bronchioles at the end of the network before reaching the alveoli. Bronchi usually branch about 20 times before they reach the alveoli.
The respiratory function of bronchi is to serve as air conductors between the atmosphere and the sites of gas exchange and the non-respiratory function is to remove foreign particles from the respiratory system.
The tubes found at the very end of tracheobronchial network are referred to as bronchioles. These tiny parts are the last segment of the tubes, through which air passes before it reaches alveoli. Unlike the bronchi, bronchioles do not have fibrocartilaginous layer. Their thinner walls are made up of smooth muscles and elastic tissue lined with ciliated epithelium. Bronchioles can be divided into two categories according to their functions; namely, non-respiratory bronchioles, which conduct air stream, and respiratory bronchioles, where gas exchange takes place.
What is the difference between Bronchi and Bronchioles?
• Trachea divides into branches forming the primary bronchi while the bronchi divide into branches forming bronchioles.
• Bronchi contain cartilaginous layer, whereas bronchioles do not.
• Respiratory function of bronchi is to serve as conductors, whereas that of bronchioles is to serve as conductors as well as the sites of gas exchange.
• Bronchi are larger in diameter than bronchioles.
• Bronchi pass the air into bronchioles, whereas bronchioles pass it into alveoli.